net: hns: Move static keyword to the front of declaration

Move the static keyword to the front of declaration of g_dsaf_mode_match,
and resolve the following compiler warning that can be seen when building
with warnings enabled (W=1):

drivers/net/ethernet/hisilicon/hns/hns_dsaf_main.c:27:1: warning:
  ‘static’ is not at beginning of declaration [-Wold-style-declaration]

Signed-off-by: Krzysztof Wilczynski <kw@linux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>